Felted ceramic fiber mats have poor strength and cannot be used as structural materials. Strength is achieved by binding the intersecting fibers with sol-gel binders, particularly those described by Yoldas in his article at 54 Ceramic Bulletin No. 3, 289-290 (1975), and curing the gelled sol to a glass. Firing the impregnated mats or catalyzing the gellation with inorganic acids or ammonia are the common methods used to gel the sol. Acid catalysts can introduce undesirable contaminants into the product. Ammonia requires that special equipment be used to isolate the processing environment.
We have discovered a simple way to gel the sol and, thereby, to form a preform composite from an impregnated felt mat. The method does not introduce impurities and does not require special equipment to protect the working environment from hazardous or toxic materials, like anhydrous ammonia.